llext: rework add_llext_target() to use standard compile step

Separate the compilation of the source file from the conversion to an
llext file. This allows to reuse the include directories and macro
definitions of the current Zephyr build while compiling the llext source.

Signed-off-by: Luca Burelli <l.burelli@arduino.cc>

cmake/modules/llext.cmake

@@ -53,34 +53,66 @@ function(add_llext_target target_name)
     DEPENDS ${output_file}
   )
 
-  # Compile the source file to an .llext file
+  # Define arch-specific flags for the supported architectures
   if(CONFIG_ARM)
     list(PREPEND LLEXT_C_FLAGS "-mlong-calls" "-mthumb")
-    add_custom_command(OUTPUT ${output_file}
-      COMMAND ${CMAKE_C_COMPILER} ${LLEXT_C_FLAGS} -c
-              -I ${ZEPHYR_BASE}/include
-              -imacros ${AUTOCONF_H}
-              -o ${output_file}
-              ${source_file}
-      DEPENDS ${source_file}
-    )
   elseif(CONFIG_XTENSA)
     list(PREPEND LLEXT_C_FLAGS "-shared" "-fPIC" "-nostdlib" "-nodefaultlibs")
+  else()
+    message(FATAL_ERROR "add_llext_target: unsupported architecture")
+  endif()
+
+  # Compile the source file to an object file using current Zephyr settings
+  # but a different set of flags
+  add_library(${target_name}_lib OBJECT ${source_file})
+  target_compile_definitions(${target_name}_lib PRIVATE
+    $<TARGET_PROPERTY:zephyr_interface,INTERFACE_COMPILE_DEFINITIONS>
+  )
+  target_compile_options(${target_name}_lib PRIVATE
+    ${LLEXT_C_FLAGS}
+    -imacros "${AUTOCONF_H}"
+  )
+  target_include_directories(${target_name}_lib PRIVATE
+    $<TARGET_PROPERTY:zephyr_interface,INTERFACE_INCLUDE_DIRECTORIES>
+    -I${PROJECT_BINARY_DIR}/include/generated
+  )
+  target_include_directories(${target_name}_lib SYSTEM PUBLIC
+    $<TARGET_PROPERTY:zephyr_interface,INTERFACE_SYSTEM_INCLUDE_DIRECTORIES>
+  )
+  add_dependencies(${target_name}_lib
+    zephyr_interface
+    zephyr_generated_headers
+  )
+
+  # Arch-specific conversion of the object file to an llext
+  if(CONFIG_ARM)
+
+    # No conversion required, simply copy the object file
+    add_custom_command(
+      OUTPUT ${output_file}
+      COMMAND ${CMAKE_COMMAND} -E copy $<TARGET_OBJECTS:${target_name}_lib> ${output_file}
+      DEPENDS ${target_name}_lib $<TARGET_OBJECTS:${target_name}_lib>
+    )
+
+  elseif(CONFIG_XTENSA)
+
+    # Generate an intermediate file name
     get_filename_component(output_dir ${output_file} DIRECTORY)
     get_filename_component(output_name_we ${output_file} NAME_WE)
     set(pre_output_file ${output_dir}/${output_name_we}.pre.llext)
-    add_custom_command(OUTPUT ${output_file}
+
+    # Need to convert the object file to a shared library, then strip some sections
+    add_custom_command(
+      OUTPUT ${output_file}
+      BYPRODUCTS ${pre_output_file}
       COMMAND ${CMAKE_C_COMPILER} ${LLEXT_C_FLAGS}
-              -I ${ZEPHYR_BASE}/include
-              -imacros ${AUTOCONF_H}
               -o ${pre_output_file}
-              ${source_file}
+              $<TARGET_OBJECTS:${target_name}_lib>
       COMMAND ${CROSS_COMPILE}strip -R .xt.*
               -o ${output_file}
               ${pre_output_file}
-      DEPENDS ${source_file}
+      DEPENDS ${target_name}_lib $<TARGET_OBJECTS:${target_name}_lib>
     )
-  else()
-    message(FATAL_ERROR "add_llext_target: unsupported architecture")
+
   endif()
 endfunction()